1. Field of the Invention
The present invention relates to a solid fuel. More specifically, it relates to a solid fuel which makes effective use of a binder, a form retaining agent and a vegetable oil-containing substance. Much more specifically, it relates to a solid fuel which makes effective use of a binder and a form retaining agent derived from natural products while using a vegetable oil-containing substance, produces as small an amount as possible of a harmful gas or residue, has a large calorific value and leads to the suppression of the production of carbon dioxide, especially a solid fuel suitable for use as a fuel for power generation.
2. Prior Art
The causes of global warming which is one of the global environmental issues include an increasing amount of carbon dioxide existent in air. Various approaches to the suppression of the production of carbon dioxide are being made on a global basis. As one of the approaches, the production of biofuels and use of them in automobiles and power boilers as alternatives to fossil fuels such as coal and gasoline are underway. However, use of foods such as corn which are used as raw materials of the biofuels is breaking down ecological balance and economical balance and therefore it cannot be said that this is the best approach. Thus, it is necessary to take the global environment into consideration while effects on clothing, food and housing whose balance is essential to human lives are minimized. Since this is a very difficult problem to be solved, various studies are under way but the problem is not solved yet. Then, a solid fuel making use of plastics is used in power boilers as an alternative to oil and coal but it cannot be said that its effect of suppressing the production of carbon dioxide is satisfactory.
Meanwhile, Patent Documents 1 to 3 propose the recycling of wood waste, paper waste and plastic waste into a solid fuel.
Patent Document 1 proposes a solid fuel which makes use of used paper and plastic waste. This solid fuel actually comprises 25 to 100 parts by weight of plastic waste based on 100 parts by weight of used paper. Thus, a relatively large amount of plastic waste (20 to 50 wt % of the total) is used. Although this Patent Document 1 teaches that a wood-based waste material may be further used, the amount of the wood-based waste material used in Examples is no more than 10 wt % of the total. The above solid fuel contains plastic waste in a relatively large proportion and therefore, the step of dechlorinating the obtained solid fuel by heating it is required to suppress a trouble caused by the inclusion of polyvinyl chloride at the time of combustion.
Patent Document 2 proposes a solid fuel obtained by pressure bonding together plastics, wooden powders, bark and used paper and molding the obtained product into a pellet. Although the amount of the plastics contained in the solid fuel is specified as 10 to 80%, judging from FIGS. 2 to 4, the amount of the plastics is estimated at 30% or more, preferably 50% or more.
Patent Document 3 proposes a method of obtaining a fuel by kneading 5 to 10 parts by weight of a synthetic resin-based waste material with 100 parts by weight of a wood-based waste material and pelletizing the kneaded product. The pellet obtained by this method has a small diameter of about 6 to 12 mm, it cannot be said that the calorific value of the pellet is sufficiently large, and further, its form retention stability is unsatisfactory. Therefore, the pellet is unsuitable for use as a solid fuel for thermal power generation.
Meanwhile, along with the frequent occurrence of a wide-scale disaster which is seemed to be caused by the global warming phenomenon in recent years, each country is trying to suppress the production of carbon dioxide which is one of greenhouse effect gases but it can be said that this is still unsatisfactory. Then, solid fuels making use of various waste products are used in power boilers as alternatives to oil and coal but it can be said that their effect of suppressing the production of carbon dioxide is still unsatisfactory.
That is, since plastics are used as a binder and a fuel source in the solid fuels proposed by the above Patent Documents 1 to 3, considering that the plastics are produced from oil, these solid fuels are unsatisfactory in the effect of suppressing the production of carbon dioxide.